What "makes" a 66 Barracuda a Formula S ??

My 65 Barracuda had the Commando 273, 4 speed, and rally suspension with HD torsion bars, HD rear springs and front sway bar. But it had 13 inch wheels and no tach. It was not a Formula S. The original 13 inch wheels got replaced long ago, and for the past 50 years it has had an aftermarket tach where the factory one would have been. Also, I put "S" badges on it years ago after a wreck that required replacing the front fenders, because I always liked the way the "S" badges looked, but now I wish it still had the Commando V8 fender badges. I still have the original fender badges, but would have to drill different holes in the fenders to mount them, plus fill the ones that are there now. So will probably just keep them as souvenirs.

The original springs were six leaf. They are in my 67 Barracuda now (originally a slant six car), while the ones in my 65 are out of the Duster 340 my brother wrecked. They also are six leaf. (The Duster springs had a lot fewer miles on them than the 65 Barracuda springs.)